FAS has never said the FM3 is the final floor unit from them. And given that there's a LOT of daylight between the power, functionality, and cost of the FM3 and the AxeFX III, I think it's a safe bet to expect a bigger brother to the FM3 in the future. Maybe not this year or next, but an FM6/8/9/etc. in the $1500-$2000 range with more power than the FM3 (but less than the AFIII) would be a no-brainer IMNSHO.
Except for the footswitches, the FM3 is a step up from the AX8 in pretty much every way. And if you really need the switches , the FC-6 or FC-12 is a GREAT expansion route for barely more $$$ than the AX8 was priced at.
I'm really trying to see the downside to the FM3 and I can't find it. I think both Line6 and FAS hit it out of the park with both of their units.